Wrist mechanism in an industrial robot

ABSTRACT

A wrist mechanism in an industrial robot comprises a wrist, a rotary type actuator which is rotatable in clockwise and counter-clockwise directions, a first positioning board which can define arbitrary angular stopping positions, sensing devices, and a second positioning board which is arranged facing the first positioning board, wherein the sensing devices detect the angular position of the wrist, which is driven by the rotary type actuator, the rotary type actuator is stopped by signals produced by the sensing devices, and the second positioning board with tapered receptacles is pressed to the first positioning board with tapered pins, whereby the positioning of the wrist mechanism is carried out.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wrist mechanism in an industrialrobot, which is used, for example, to treat work piece materials formachine tools.

2. Description of the Prior Art

In one prior art device, a wrist mechanism in an industrial robot hasbeen used in which the angular positioning for any desired position iscarried out with a servo control device. However, the servo controldevice is very expensive; thus the servo control device has not beenwidely used in this field.

In another prior art device, a wrist mechanism in an industrial robothas been used in which the angular positioning is carried out with theangular positioning device for two positions. The device, for example,comprises a rotary type actuator having two air intakes. The rotor ofthe rotary type actuator rotates clockwise when the air pressure isapplied to one of the air intakes and the rotor rotates counterclockwisewhen the air pressure is applied to the other air intake. A pawl isprovided coaxially with the rotor of the rotary type actuator and stopsthe rotor at desired angular positions cooperating with stoppers, whichare located on the outer portion of the stator of the rotary typeactuator, so that the angular positioning of the wrist mechanism of anindustrial robot, which is linked with the rotor of the rotary typeactuator, is carried out. An angle between two stopping positions of thewrist mechanism is decided by the relation of the shape of the pawl andthe positions of the stoppers.

In recent years, the necessity of various positions, for example,positions of angles of 0 degree, 90 degrees, 180 degrees and 270 degreesfrom the reference position, is required frequently because ofapplications in which the wrist mechanism has double grasping portions,the necessity of working both a front surface and a back surface, andthe relations of the locations between the work and the work locatingbase or the work transferring device. For the above mentioned fourpositions, hitherto a wrist mechanism using the conventional servocontrolled positioning was utilized, or two angular positioning devicesfor two positions was utilized, putting the devices one upon another.For these reasons, problems exist in the conventional wrist mechanisms,in that the cost of the wrist mechanism becomes very expensive and thewrist mechanism is not practical, because of the large size of themechanism compared with the functions thereof. The wrist mechanism usingthe angular positioning device for two positions comprising the rotarytype actuator was disclosed in U.S. Pat. No. 4,274,802, issued June 23,1981, by the inventor of the present invention.

The present invention is proposed to solve the above mentioned problemsin conventional wrist mechanisms.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an improved wristmechanism in which an angular multi-positioning is able to be carriedout accurately and directly for predetermined angular positions.

According to the present invention, there is provided a wrist mechanismin an industrial robot comprising a wrist, a rotary type actuatorrotatable in clockwise and counter-clockwise directions for actuatingthe wrist, a first positioning board having tapered pins and aprojection, sensing devices associated with the projection, and a secondpositioning board having tapered receptacles for receiving the taperedpins, wherein the sensing devices are adapted to detect the angularposition of the wrist, the rotary type actuator is adapted to be stoppedby signals produced by the sensing devices, the second positioning boardis adapted to be pressed to the first positioning board whereby thepositioning of the wrist mechanism is carried out.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating the construction of awrist mechanism of an industrial robot according to an embodiment of thepresent invention;

FIG. 2 is a plan view illustrating the construction of the secondpositioning board in the wrist mechanism of FIG. 1;

FIG. 3 is a fragmentary view taken in the direction of the arrows alongthe line III--III of FIG. 1;

FIG. 4 is an operational diagram in the wrist mechanism of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 1 through 4 are diagrams illustrating a wrist mechanism of anindustrial robot according to an embodiment of the present invention.FIG. 1 is a cross-sectional view of the wrist mechanism. The wristmechanism comprises a wrist 13, a rotary type actuator 11, a graspingmember 12, a first positioning board 33, a second positioning board 35with tapered receptacles 351, sensing devices 62, a piston 36 of aircylinder and a casing 38. The rotary type actuator may be a conventionalone, has two compressed air intakes and a rotor, and can rotate therotor either clockwise or counterclockwise by the connection ordisconnection of the compressed air to the intake pipes of the actuator.The rotary axis of the rotary type actuator 11 is coaxial with those ofthe grasping member 12, the wrist 13 and the first positioning board 33.The grasping member 12 is a member in which a material to be processedis grasped and in FIG. 1 a schematic representation of the graspingmember 12 is shown.

The first positioning board 33 in the embodiment of the presentinvention, as shown in FIG. 3, is constructed with a circular plate, twotapered pins 331 peripheral projection 61. The tapered pins and theprojection 61 are attached on the circular plate. The projection 61 isan actuator to switch on limit switches to supply signals of the angularpositioning of the wrist mechanism.

As shown in FIG. 1, the outer cylindrical portion of the rotary typeactuator 11 is coupled to the casing 38 which accommodates the firstpositioning board 33 and the second positioning board 35. In addition,the casing 38 accommodates the guide pins 34, air pressing piston 36 bywhich the second positioning board 35 is pressed to slide along theguide pins, and a spring 37 which presses the second positioning board35 to the first positioning board 33. FIG. 2 is a plan view of thesecond positioning board 35.

FIG. 4 is an operational diagram of the wrist mechanism, in which theposition controller that electrically interconnects the mechanicalelements of the invention is shown purely schematically. Each of thesensing devices or limit switches 62 is positioned within casing 38 tobe engaged by projection 61 at a desired stopping position where thetapered pins 331 are alinged with a pair of the tapered receptacles 351,and another limit switch 54 is actuated by board 35 when it is moved tothe left so that pins 331 are fully engaged into tapered receptacles351.

In operation, the position controller operates the elements in thefollowing sequence to move the wrist from a present position to a newposition:

Step 1--magnetic valve 53 is energized to move to the left,disconnecting air pressure source 56 from line 531 and connecting it toline 532, thus applying pressure to the left side of piston 36 andmoving it to the right on guide pins 34 against spring 37, therebymoving positioning board 35 away from board 33 to disengage receptacles351 from pins 331.

Step 2--magnetic valve 51 is energized to move to the right,disconnecting air line 511 from air pressure source 55 and venting it toth atmosphere while air line 521 remains connected, allowing the rotaryactuator to be operated by air pressure from source 55 through valve 52and line 521.

Step 3--the position controller senses when the sensing device 62 forthe desired position is actuated by projection 61, and energizesmagnetic valve 52, moving it to the left. This disconnects air pressuresource 55 from air line 521 and vents that line to the atmosphere,equalizing pressure in rotary actuator 11 and stopping it at thatposition.

Step 4--magnetic valve 53 is deenergized and returns to its originalposition as shown in FIG. 4, connecting air pressure from source 56 toline 531 and applying pressure to the right side of piston 36, whichtogether with spring 37, moves piston 36 to the left and brings thetapered receptacles 351 on board 35 into engagement with tapered pins331 on boards 33 to accurately position the wrist and hold it in thatposition.

Step 5--when board 35 is moved so that pins 331 are fully engaged inreceptacles 351, switch 54 operates. The controller senses theconcurrent operation of sensing elements 62 and switch 54, confirmingaccurate positioning of the wrist, and deenergizes magnetic valves 51and 52, permitting them to return to their original positions, therebypreparing the system for the next cycle.

When the electric power is interrupted or the air pressure is decreased,the wrist does not rotate because the second positioning board 35 ispressed to the first positioning board 33 the spring 37 located in theair cylinder and held in this position.

Furthermore, in the present invention the wrist is movable directly tothe desired position without stopping at any other positions as in theconventional mechanism. Thus the unnecessary action of stopping andstarting on the way is not performed and wrist positioning is carriedout quickly. Also, the angular positionings of the wrist mechanism isperformed through the shortest course by being able to be moved eitherclockwise or counter-clockwise, which appropriate utilization preventsthe twisting of the cables or air tubes by which the wrist mechanism isconnected with power sources and so on.

We claim:
 1. An industrial robot wrist mechanism positionable to aplurality of predetermined positions, comprising:a rotatable wristmember; a rotary actuator having a rotor movable about an axis under theinfluence of fluid pressure, said wrist member being fixed to said rotorfor movement therewith; a casing affixed to said rotary actuator; afirst board positioned within said casing and fixed to said rotatablemember for rotation therewith, said first board having a pair of taperedpins extending axially therefrom and a peripheral projection extendinglaterally therefrom; a plurality of sensing devices fixed adjacent tosaid first board within said casing and arranged to detect a pluralityof angular positions of said projection about said axis; a second boardmounted to be rotatively fixed and axially movable within said casing,said second board being formed with a plurality of tapered receptaclesarranged to receive said tapered pins in different rotational positionsof said first board; a fluid operated piston connected to said secondboard and operable to move said second board axially with respect tosaid first board; a first magnetic valve for controlling fluid flow froma first source of fluid pressure to said piston, and second and thirdmagnetic valves for controlling the fluid flow from a second source offluid pressure to said rotary actuator; said valves being so connectedthat energization of said first magnetic valve will cause fluid fromsaid first source to operate said piston to move said second boardaxially away from said first board and disengage said pins from saidreceptacles, whereafter energization of said second magnetic valve willallow fluid from said second source to operate said rotary actuator torotate said rotor together with said wrist member and said first boarduntil said projection is detected by a selected one of said sensingdevices, whereupon energization of said third magnetic valve willdisconnect said rotary actuator from said fluid source to cause saidrotor to stop, and thereafter deenergization of said first valve willcause fluid from said first source to operate said piston axially tomove said second board toward said first board and engage said taperedpins into a selected pair of said receptacles, whereby angularpositioning of said wrist member is carried out.